Amide-imide polymers and copolymers are a relatively new class of organic compounds known for their solubility in nitrogen-containing solvents when in the largely polyamide form. In the past, the major application of these amide-imide polymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,661,832 (1972), 3,494,890 (1970) and 3,347,828 ( 1967). Amide-imide polymers and copolymers have also been found useful in molding applications as shown in U.S. Pat. Nos. 4,016,140 (1977) and 3,573,260 (1971). Both are incorporated herein by reference. These polyamides are known for their outstanding mechanical properties, but they are also difficult to process.
Using prior art processes, it has been impossible to extrusion mold thin films, thin sheets, and thick sheets from these polyamide-imides or to produce thick parts used as tubes and pipes. The art has been looking for useful extrusion processes to manufacture films, having a thickness of about 1 to about 15 mils, from these polyamide imides, and thin sheets of about 10 to about 250 mil thickness. Likewise, the art has been looking to produce tubes and pipes having a wall thickness of about 0.05 inches to about 0.25 inches and with outside diameter of about 0.25 inches to about 2 inches made from polyamide-imides.
The general object of this invention is to provide an extrusion molding process for the manufacture of molded products which cannot be prepared by injection molding or by extrusion processes known in the prior art. A particular object of this invention is to provide a process for the extrusion of thin films, having a thickness of about 1 to about 15 mils, the extrusion of thin sheets, having a thickness of about 10 to about 250 mils, and the extrusion of hollow tubes with outside diameters of about 0.25 inches to about 2 inches and a wall thickness of about 0.05 inches to about 0.25 inches are also objects of this invention.
A more specific object is to provide a process for extruding thin films and thick tubes and pipes by extruding the amic acid and amide-imide polymer through melt channels and extrusion dies at continuously increasing shear rates and at temperatures of about 575.degree. F. to about 680.degree. F.